The sickle RBC membrane abnormality that is most clearly implicated in sickle disease pathophysiology is that defect which confers abnormal cation homeostasis and, ultimately, leads to cellular dehydration. The present studies will examine a novel potassium leak pathway that reflects synergistic adverse effects of peroxidation and cellular deformation. The model to be used is that of elliptical deformation of oxygenated normal and peroxidatively-perturbed RBC. This deformation is achieved by application of shear stress to RBC in viscous suspending medium using a concentric cylinder viscometer. Five aims will be pursued. First, to clarify what aspects of peroxidative damage are responsible for the synergistic leak pathway, we will dissect peroxidative damage into its various component parts using selective manipulations of normal RBC to see if they simulate the synergistic leak. Second, we will examine the biophysical characteristics of this synergistic potassium leak pathway observed during peroxidation-plus-deformation. Some studies will use micromechanical methods to examine the cohesiveness and material properties of liposomes reconstituted from RBC membrane lipid extracts. Other studies will examine the ion selectivity (if any) of the synergistic leak pathway, as well as relevant activation energies and pore size and number per cell that develop. Direct comparison will be made with oxygenated and deoxygenated sickle RBC. Third, the possible relevance of this leak pathway to calcium homeostasis will be examined as will a possible threshold (of peroxidation) beyond which the synergistic leak pathway develops a calcium-dependence. Fourth, we will determine whether this leak pathway is exposed in deforming sickle RBC themselves. This will be addressed by examining K+ leak during elliptical deformation of oxygenated sickle RBC and during deoxygenation-induced deformation of normal (or perturbed) RBC membranes reversibly loaded with HbS. Finally, we will determine whether correlative data support a relationship between autoxidative damage in sickle RBC and development of the synergistic, peroxidation-plus-deformation K+ leak pathway. In aggregate, these studies will fully define this synergistic leak pathway and determine whether it is operative in sickle RBC (and is, therefore, a potential contributor to sickle RBC dehydration).